This invention relates to fittings for high voltage purposes, such as prefabricated push-on control elements in general and more particularly to fittings for high voltage cables.
In high voltage apparatus, the need to control the electric field between the high voltage and ground in order to equalize sudden transitions and field strength peaks connected therewith frequently arises. In this connection, the so-called capacitive field control method, in which several electrodes are staggered relative to each other and where the first electrode is at ground potential and the last electrode is approximately at high voltage potential, is frequently used. Such capacitive field controls are customary, for instance, in high voltage feedthroughs and in fittings for high voltage cables.
In the mechanical design of fittings for high voltage cables, a transition to prefabricated parts which can merely be slipped onto the appropriately prepared cable end, by being expanded elastically, has been made to simplify the installation work. Thus, a prefabricated plug-on end termination for high voltage cables is known, for instance, which consists of several stacked insulators with deflectors of conductive material embedded in the insulating bodies. The individual parts of the termination can be made of silicone rubber (DE-OS No. 26 06 238).
For controlling the electric field in terminations of medium voltage cables, elastic insulators which contain only a single deflector are used. This deflector may be a prefabricated component, around which a cross-linkable silicone rubber compound is cast to manufacture the complete control element or the push-on fitting element (DE-AS No. 26 43 197, Nov. 24, 1977). The deflector (cone), however, can also consist of a homogeneous layer of an expandable electrically conductive material which is applied to an elastic cone carrier and is cemented to an elastic termination (DE-AS No. 14 90 115, July 3, 1969).
Starting out from a prefabricated control element which can be elastically expanded radially, for controlling the electric field in high voltage apparatus, especially in fittings of high voltage cables, which can be slipped onto a bare or insulated conductor and consists of several elastic insulators which follow each other in the axial direction and engage each other and are provided with funnel shaped end faces, and with which electrically conductive parts of likewise electric material are associated which together form a capacitive control, it is an object of the present invention to improve its dielectric strength by making the entire control element of one piece.